This application claims benefit of German application DE 101 32 718.8, filed Jul. 5, 2001 in Germany.
1. Field of the Invention
The present invention relates to magnetic-induction devices such as electrical-power transformers. More specifically, the invention relates to the manufacture of an electrical-power transformer having phase windings formed from insulated conductive cabling.
2. Background of the Invention
Electrical-power transformers are used extensively in electrical and electronic applications. Transformers transfer electric energy from one circuit to another circuit through magnetic induction. Transformers are utilized to step electrical voltages up or down, to couple signal energy from one stage to another, and to match the impedances of interconnected electrical or electronic components. Transformers are also used to sense current, and to power electronic trip units for circuit interrupters. Transformers may also be employed in solenoid-equipped magnetic circuits, and in electric motors. The term xe2x80x9cdistribution transformerxe2x80x9d is used to describe electrical-power transformers having power ratings of approximately 50 kVA to approximately 2,000 kVA; distribution transformers typically have high-voltage windings rated at approximately 10 kV to approximately 20 kV.
A typical electrical-power transformer includes two or more multi-turned coils of wire commonly referred to as xe2x80x9cphase windings.xe2x80x9d The phase windings are placed in close proximity so that the magnetic fields generated by the windings are coupled when the transformer is energized. Most electrical-power transformers have a primary winding and a secondary winding. The output voltage of a transformer can be increased or decreased by varying the number of turns in the primary winding in relation to the number of turns in the secondary winding.
The magnetic field generated by the current passing through the primary winding is typically concentrated by winding the primary and secondary windings on a core of magnetic material. More particularly, the primary and secondary windings are placed on one or more winding legs of the core. This arrangement increases the level of induction in the primary and secondary windings so that the windings can be formed from a smaller number of turns while still maintaining a given level of magnetic-flux. In addition, the use of a magnetic core having a continuous magnetic path ensures that virtually all of the magnetic field established by the current in the primary winding is induced in the secondary winding.
An alternating current flows through the primary winding when an alternating voltage is applied to the winding. The value of this current is limited by the level of induction in the winding. The current produces an alternating magnetomotive force that, in turn, creates an alternating magnetic flux. The magnetic flux is constrained within the core of the transformer and induces a voltage across the secondary winding. This voltage produces an alternating current when the secondary winding is connected to an electrical load. The load current in the secondary winding produces its own magnetomotive force that, in turn, creates a further alternating flux that is magnetically coupled to the primary winding. A load current then flows in the primary winding. This current is of sufficient magnitude to balance the magnetomotive force produced by the secondary load current. Thus, the primary winding carries both magnetizing and load currents, the secondary winding carries a load current, and the core carries only the flux produced by the magnetizing current.
FIG. 1 depicts a three-phase distribution transformer 100 of conventional design. The transformer 100 comprises a magnetic core 101. The magnetic core 101 comprises a first winding leg 102, a second winding leg 104, and a third winding leg 106. The transformer 100 also comprises an upper yoke 108 and a lower yoke 110. The winding legs 102, 104, 106 and the upper and lower yokes 108, 110 each comprise a plurality of laminae 120 formed from a suitable magnetic material such as textured silicon steel or an amorphous alloy. The winding legs 102, 104, 106 and the upper and lower yokes 108, 110 are each formed by stacking (superposing) a respective set of laminae 120 to a predetermined depth and binding the laminae 120 using a suitable means such as adhesive.
Opposing ends of the winding legs 102, 104, 106 are fixedly coupled to the upper and lower yokes 108, 110 using a suitable means such as adhesive. A cylindrical phase winding 112 is positioned on each of the winding legs 102, 104, 106. Each phase winding 112 comprises a low-voltage primary winding 112a and a concentric, high-voltage secondary winding 112b located radially outward of the primary winding 112a. The primary and secondary windings 112a, 112b are each formed by multiple layers, or coils, of conductive cabling connected in series. Each layer is formed by a plurality of turns of the conductive cabling connected in series.
The conductive cabling used to form the phase windings 112 is typically non-insulated cabling. The use of non-insulated cabling necessitates the placement of an electrically-insulative material within the phase windings 112. More particularly, a solid, electrically-insulative material such as epoxy resin is typically placed between adjacent turns, and between adjacent layers within the phase winding 112. (The phase windings of oil-filled transformers are further insulated by the mineral oil that surrounds the phase windings within such transformers.)
The placement of insulation between the adjacent turns and layers of the phase winding 112 is necessary to prevent short-circuiting that would otherwise occur due to the differing electric potential between the adjacent layers and turns. Insulation is also necessary to prevent short circuiting between adjacent phase windings 112, and between the phase windings 112 and adjacent conductive components. The solid insulative material is placed individually over each cable layer, and between adjacent turns in the particular layer, immediately after the layer has been wound. Hence, installation of the solid insulative material must be integrated into the winding process for each phase winding 112.
The phase winding 112 can alternatively be formed from insulated conductive cabling (as shown in FIG. 1). For example, PCT application serial no. PCT/SE/9700875 (international publication no. WO 97/45847) discloses a transformer winding formed from an insulated conductive cable having an inner conductor surrounded by a concentric layer of semi-conductor material. The layer of semi-conductor material is surrounded by a concentric layer of solid insulative material. The layer of solid insulative material is surrounded by a concentric second layer of semi-conductor material that forms the outermost portion of the cable. Forming a phase winding from insulated conductive cabling eliminates the need to install additional solid insulative material within the phase winding as the phase winding is wound. Another example of insulated conductive cabling suitable for use in forming the phase winding 112 is disclosed in pending U.S. patent application Ser. No. 09/541,523, filed Apr. 3, 2000, which is incorporated herein by reference in its entirety.
The transformer 100 may be manufactured in accordance with the following conventional process. The phase windings 112 are formed using a suitable mandrel. More particularly, the mandrel is assembled, a primary winding 112a is wound thereon, and the corresponding secondary winding 112b is wound over the primary winding 112a. The mandrel is subsequently disassembled to permit removal of the completed phase winding 112 therefrom. This process is repeated until the phase windings 112 for each of the winding legs 102, 104, 106 have been completed.
The winding legs 102, 104, 106 are fixedly coupled to the lower yoke 110 (the resulting assembly is commonly referred to as an xe2x80x9cE-corexe2x80x9d). Each completed phase winding 112 is subsequently placed over a respective winding leg 102, 104, 106, and may be secured to the winding leg 102, 104, 106 by a suitable means such as brackets 107. The upper yoke 108 is then fixedly coupled to the winding legs 102, 104, 106.
An alternative conventional manufacturing process for the transformer 100 comprises placing the winding legs 102, 104, 106 in a suitable winding machine individually, winding the primary windings 112a directly on the winding legs 102, 104, 106, and then winding the secondary winding 112b on each primary winding 112a. The upper and lower yokes 108, 110 are subsequently coupled to the winding legs 102, 104, 106. The presence of the phase windings 112 on the winding legs 102, 104, 106 usually necessitates the use of a suitable fixture to support the winding legs 102, 104, 106 as the upper and lower yokes 108, 110 are joined thereto.
Each of the above-described activities adds to the time and expense associated with manufacturing the transformer 100. For example, the use of a mandrel to form the phase windings 112 requires the assembly and disassembly of the mandrel each time a phase winding 112 is formed. Winding the phase windings 112 directly on the winding legs 102, 104, 106 in the alternative process requires that each winding leg 102, 104, 106 be installed in and removed from a winding machine, and then placed in a support fixture so that the upper and lower yokes 108, 110 can be joined thereto. In addition, the stresses imposed on the winding legs 102, 104, 106 require that the laminae 120 that form the winding legs 102, 104, 106 be bound together more strongly than would otherwise be required.
Both of the above-described processes for assembling the transformer 100 require that the phase windings 112 be installed on the winding legs 102, 104, 106 prior to final assembly of the magnetic core 101. This requirement represents a disadvantage because manufacture of the magnetic core 101 and final assembly of the transformer 100 often take place at different locations. Shipping the magnetic core 101 from its place of manufacture to the final assembly location usually necessitates installing the upper yoke 108 on the assembled E-core on a temporary basis. The upper yoke 108 is subsequently removed from the E-core to facilitate installation of the phase windings 112. The upper yoke 108 is coupled to the winding legs 102, 104, 106 on a final basis after the phase windings 112 have been installed.
Neither of the above-described manufacturing processes are particularly advantageous when used in connection with a transformer having windings formed from insulated conductive cabling. In particular, insulated conductive cabling can be wound into a phase winding such as the phase winding 112 without a need to integrate a separate insulative material into the winding, as noted previously. Neither of the above-described processes offer manufacturing advantages that stem from this feature.
A need therefore exists for a process for manufacturing an electrical-power transformer that requires fewer activities and less equipment than a conventional assembly process. A manufacturing process that permits final assembly of the core without the corresponding phase windings installed thereon is desirable. A manufacturing process that provides advantages associated with the unique manufacturing characteristics of phase windings formed from insulated conductive cabling is also desirable.
A presently-preferred process for manufacturing an electrical-power transformer comprises stacking a plurality of laminae to form a first, a second, and a third winding leg and an upper and a lower yoke, and fixedly coupling the first, second, and third winding legs to the lower yoke. The presently-preferred process also comprises winding a first length of insulated conductive cabling on the first winding leg to form a first phase winding, winding a second length of the insulated conductive cabling on the second winding leg to form a second phase winding, and winding a third length of the insulated conductive cabling on the third winding leg to form a third phase winding after coupling the first, second, and third winding legs to the lower yoke. The presently-preferred process further comprises fixedly coupling the first, second, and third winding legs to the upper yoke after forming the first, second, and third phase windings.
Another presently-preferred a process for manufacturing an electrical-power transformer comprises stacking a plurality of laminae to form a first, a second, and a third winding leg and an upper and a lower yoke. The presently-preferred process also comprises fixedly coupling the first, second, and third winding legs to the lower yoke, and fixedly coupling the first, second, and third winding legs to the upper yoke. The presently-preferred process further comprises winding a first length of insulated conductive cabling on the first winding leg to form a first phase winding, winding a second length of the insulated conductive cabling on the second winding leg to form a second phase winding, and winding a third length of the insulated conductive cabling on the third winding leg to form a third phase winding after coupling the first, second, and third winding legs to the upper and lower yokes.
A presently-preferred process for manufacturing a magnetic-induction device comprises forming a plurality of laminae from a sheet of magnetic material, stacking the plurality of laminae to form a winding leg, a first yoke, and a second yoke, and fixedly coupling a first end of the winding leg to the first yoke. The presently-preferred process also comprises winding a length of insulated conductive cabling on the winding leg to form a phase winding after fixedly coupling the winding leg to the first yoke, and fixedly coupling a second end of the winding leg to the second yoke after forming the phase winding.
Another presently-preferred process for manufacturing a magnetic-induction device comprises forming a plurality of laminae from a sheet of magnetic material, stacking the plurality of laminae to form a winding leg, a first yoke, and a second yoke, and fixedly coupling a first end of the winding leg to the first yoke. The presently-preferred process also comprises fixedly coupling a second end of the winding leg to the second yoke, and winding a length of insulated conductive cabling on the winding leg to form a phase winding after fixedly coupling the winding leg to the first and second yokes.
Another presently-preferred process for manufacturing an electrical-power transformer comprises assembling an E-core. The presently-preferred process also comprises winding a first length of insulated conductive cabling on a first winding leg of the E-core to form a first phase winding, winding a second length of the insulated conductive cabling on a second winding leg of the E-core to form a second phase winding, and winding a third length of the insulated conductive cabling on a third winding leg of the E-core to form a third phase winding after assembling the E-core. The presently-preferred process further comprises fixedly coupling an upper yoke to the E-core after forming the first, second, and third phase windings.
Another presently-preferred process for manufacturing an electrical-power transformer comprises assembling a magnetic core. The presently-preferred process also comprises winding a first length of insulated conductive cabling on a first winding leg of the magnetic core to form a first phase winding, winding a second length of the insulated conductive cabling on a second winding leg of the magnetic core to form a second phase winding, and winding a third length of the insulated conductive cabling on a third winding leg of the magnetic core to form a third phase winding after assembling the magnetic core.